Safety fuse with time and impact action

ABSTRACT

A safety fuse, preferably usable for light grenades and shells having combined time and impact action, comprising a main piston containing elements of the ignition chain, said piston being displaced radially in a bore in the fuse casing by a driving spring, the time of this movement being prolonged by the vacuum created behind the ring-tightened piston, said vacuum being adjustable by leak holes having an arbitrary diameter. The fuse also contains a delay-composition-containing piston that is movable toward a fixed firing pin in a direction at an angle to the main piston. The delay piston has stopping means preventing its movement as long as the main piston has not reached its outward, fully armed position.

Unite States Patent [72] Inventor Claes G. Arnell 3,078,802 2/1963Sturrock 102/72 Torshalla, Sweden 3,313,236 4/l967 Lohmann 102/72 [2i]Appl. No. 36,170 3,371,608 3/1968 Webb lO2/72 [221 Ned May 1970 PrimaryExaminer-SamuelW. Engle [45] Patented 1971 Attorney-Munson & Fiddler[73] Assignee Forsvarets Fariksverk Eskilstuna, Sweden [32] Priority May10, 1969 [33] Sweden [3l] 7026/69 [54] SAFETY FUSE TIME AND IMPACTACTION ABSTRACT: A safetv fuse, preferably usable for light 4 Claims, 2Drawing Figs grenades and shells having combined time and impactac tion,comprising a main piston containing elements of the ignition [52] U.S.Cl 102/72, chain, Said piston being displaced n in a bore in the f102/78. 02/855 casing by a driving spring, the time of this movementbeing [51] B e v r 9/10 prolonged by the vacuum created behind thering-tightened [50] Field of Search lO2/7l, 72, piston, Said vacuumbeing adjustabre by leak ho|e5 having an 78, 80v arbitrary diameter. Thefuse also contains a delay-composition-containing piston that is movabletoward a fixed firing pin {56] References Cited in a direction at anangle to the main piston. The delay piston UNITED STATES PATENTS hasstopping means preventing its movement as long as the 2,005,053 6/1935Schlafer 102/72 main piston has not reached its outward, fully armedposition.

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INVENTOR l it ,4 CLAES G. ARNELL BY MUNSON & FIDDLER ATTORNEY SAFETYFUSE WITH TIME AND IMPACT ACTION Fuses for antiaircraft shells usuallyhave an impact-sensitive circuit and a time-sensitive circuit thatstarts to work if the shell misses the target, resulting inself-destruction. Such fuses are known and are shown in US. Pat. Nos.3,078,802 and 3,371,608. The hammer and firing pin units shown have aconically shaped bore containing a ball that transmits the retardationduring impact to the hammer independent of the direction of impact suchas by a ball and cone striker. US. Pat. No. 3,371,608 discloses amovable piston containing a delay composition that is thrown against afixed firing pin when the projectile is brought to rotation duringlaunch.

The present invention relates to a fuse of this type that has a pistonprovided with a special safety ball lock where the piston prevents thetime circuit from not releasing until the piston has had sufficient timeto move to a position where the firing pin in the impact circuit canreach the percussion cap and the booster. The fuse is especially suitedfor hand and smoke grenades and in particular grenades that can beattached to a rear driving part having stabilizing fins enabling thegrenades to be launched by a small mortar.

The accompanying drawing discloses an embodiment of the invention and inwhich FIG. 1 shows a main section parallel with the axis of the pistonand FIG. 2 shows a sectional view taken perpendicular to said axis.

In the drawing is shown a fuse casing 1 having a transverse bore 20 inwhich a main piston 7, surrounded and sealed by double O-rings, isfitted. The main piston 7 is preferably spring loaded by springs 30 andat one end is pierced by a hole containing a percussion cap. The cap isshown at Ma and a booster 14b and the cap are fully displaced inrelation to a detonator when the piston 7 is pushed into the bore 20.The detonator is located in the center of a cover 11 that is sealed byan O-ring 21 and it covers a hole extending through the top wall of thecasing. A TNT charge 10 is located above the cover 11 and the booster.Attached in the cover is a fixed firing pin 12 (FIG. 2) and a smallpermanent magnet 9 that holds a ball 9a that is capable of movementthrough a second hole in the top wall of the fuse casing. The ball 9aprojects down into the upper widened part 8a of a radial bore in thepiston 7 and said bore has a shoulder indicating the transition to adeeper, lower part 8b of the bore, said part 8b having the same diameteras the ball. The fuse casing I has, parallel to its axis, a holecontaining another piston 13 (FIG. 2) that is spring loaded from belowby spring 23 and is filled with a delay composition. This is a timecircuit piston and it has a stopping flange 1311 that abuts against thejacket of the main piston 7 except when the piston 7 is in a fullydrawn-out, armed position. The main piston 7 has at its underside, arecess 6b for the purpose of catching the firing pin before the piston 7has had enough time to move out to fully armed position. The piston 7also has in its externally projecting end, a hole for atransport-locking sprint 7a that prevents the piston from being pushedin unintentionally. Finally, the main piston 7 can have at least onesmall leak hole [7 for air going radially into the guiding hole for themain piston spring 30. The diameter of this hole regulates the durationof time for the outward arming movement of the piston together with thedriving spring pressure.

Just under the main piston 7 there is a transversely directed hole 24 inthe fuse casing for a locking pin 15, sealed with an O-ring and providedwith a handle 25 directed at an angle. The end of the locking pin remotefrom the handle has a U- shaped recess 26 into which a movable firingpin 6 penetrates through a central guiding hole 27 in the bottom wall ofthe fuse casing. The firing pin 6 has a head and is shaped like a thumbtack and it abuts directly against a relatively large metal ball 5located in a conical, funnel-shaped bore provided with a permanentmagnet 3 in its bottom in an adjacent bottom socket 2 that is threadedinto the lower part of the fuse casing l. The socket 2 is externallythreaded and can be equipped with either a protective cap or a shorttube 4 or tail, with a driving charge and guiding fins underneath. Insuch a form the fuse can be used in wing shells for a small portablemortar with a range of a couple of hundred yards.

The operation of the fuse is substantially as follows:

If used in a handgrenade where both delay and impact action are desiredthe transport safety or spring 7a and the striker operation or lockingpin 15 are both removed. The user then manually pushes the main piston 7inwardly and when he later launches the grenade the ball 5 will overcomethe attraction of the magnet 9 by this movement and the ball 5 fallsdown from the mouth into the bottom of the bore 8b in the main pistonthat is now free to move outwardly. This outward movement takesapproximately from 1 to 1.5 seconds because of the strong suction orvacuum effect behind the piston 7 and the air will only leak in throughthe small hole 17. The piston is halted in the armed position by meansof a small peg l6 positioned in the bottom wall of the casing l andwhich pin strikes against one end of a recess or shallow groove or slot16a formed in the lower part of the piston 7. The flange 13a on thepiston 13 that contains the delay composition, is now able to passthrough a corresponding recess or cutaway part in the jacket of the mainpiston 7 with the result that the piston 13 strikes against the fixedstriker pin 12 in the cover 11. The gages from the ignited delaycomposition will leak out through and along the groove or slot 16abecause the O-ring at the right end of the piston will be outside theexternal wall of the fuse casing. After about 3 seconds a flashover tothe percussion cap 14a will take place and the grenade will explode. Ifthe grenade should make an impact before flashover from the outburneddelay charge, the ball 5 will push the firing pin 6 into the percussioncap 14a but if the user happens to drop the grenade before launch, thepiston will not have had enough time to move fully outwardly beforeimpact with the result that the firing pin 6 will only enter the recess6b, rendering the grenade harmless.

If the impact striker action is not desired, the striker safety, thelocking pin 15, can be allowed to stay in the fuse at launching.

If the fuse is to be used in an ammunition round in a light mortar thereis often no need for delayed action and the piston 13 can therefore belocked by any conventional lock. The transport and striker functionsafety (7a and 15 respectively) are removed as herein described and thegrenade is introduced into the mortar barrel after the driving tail parthas been threaded on. The gas pressure during launch will push thepiston 7 inwardly with a force much greater than if one uses hand powerand the ball 9a will be moved down into the bore 8b due to the linearacceleration. The piston does not start to move-outwardly until thegrenade has left the barrel but after that there is obtained anunusually long trajectory safety. That is tosay, the grenade travels along distance from the gun muzzlebefore the fuse is fully armed.

What is claimed is:

l. A safety fuse having combined delay and impact-type action andpreferably adapted for a hand or smoke grenade, said fuse containing afiring pin actuated by an impact-sensitive body located in an adjacentbottom socket attached to a fuse casing and comprising a conicalfunnellike surface, a permanent magnet, a percussion cap, a boostercharge, a transversely movable main piston in the casing, the boostercharge being located in the piston, the piston being spring loaded andfitted in a bore in the casing, the casing having a second bore, thelatter bore containing a spring-loaded, delay-compositioncontainingpiston, a fixed firing pin toward which the latter piston is movable,the main piston when in a safety position being prevented from movingoutwardly, a locking body preventing such movement, said locking bodypartly resting in a hollow in the casing, a magnet mounted in a coverover the hole and holding the locking body in place, the main pistonhaving a radial bore into which the locking body partly projects, saidbore having a narrowed portion, the main piston being pushed inwardly inthe casing when the fuse is subjected to a small acceleration force suchas occurs in launching, such movement causing release of the lockingbody and permitting the movement of the locking body into the narrowedportion of the radial bore, the delay composition piston having a flangethat passes a cutaway part of the main piston when the latter hasreached its fully armed position with the percussion capjust in front ofthe firing pin.

2. A safety fuse according to claim 1, wherein the main piston is sealedby O-rings and is provided with at least one leak hole extending into aguide hole for the piston-biasing spring on the rear side of the mainpiston in order to clear the subpressure created behind the main pistonwhen it is being brought to armed position whereby, except for thepiston spring pressure. the diameter of said leak hole determines thedelay time of the arming movement.

3. A safety fuse according to claim 2, wherein the fuse casing has ahole on a level with an end of the firing pin for a sidewardlydisplaceable locking pin having a recess for the reception in safetyposition of the firing pin which has the lowest possible mass, saidlocking pin having a head abutting directly against the impact-sensitivebody as long as the locking pin striker functions safety stays in.

4. A safety fuse according to claim 1, wherein a short tube with a hole,fins and driving charges can be attached to a bottom socket of the fuseand that the main piston is pushed inwardly by the pressure of thedriving gases in the barrel of a mortar during launch.

1. A safety fuse having combined delay and impact-type action andpreferably adapted for a hand or smoke grenade, said fuse containing afiring pin actuated by an impact-sensitive body located in an adjacentbottom socket attached to a fuse casing and comprising a conicalfunnellike surface, a permanent magnet, a percussion cap, a boostercharge, a transversely movable main piston in the casing, the boostercharge being located in the piston, the piston being spring loaded andfitted in a bore in the casing, the casing having a second bore, thelatter bore containing a spring-loaded, delay-composition-containingpiston, a fixed firing pin toward which the latter piston is movable,the main piston when in a safety position being prevented from movingoutwardly, a locking body preventing such movement, said locking bodypartly resting in a hollow in the casing, a magnet mounted in a coverover the hole and holding the locking body in place, the main pistonhaving a radial bore into which the locking body partly projects, saidbore having a narrowed portion, the main piston being pushed inwardly inthe casing when the fuse is subjected to a small acceleration force suchas occurs in launching, such movement causing release of the lockingbody and permitting the movement of the locking body into the narrowedportion of the radial bore, the delay composition piston having a flangethat passes a cutaway part of the main piston when the latter hasreached its fully armed position with the percussion cap just in frontof the firing pin.
 2. A safety fuse according to claim 1, wherein themain piston is sealed by O-rings and is provided with at least one leakhole extending into a guide hole for the piston-biasing spring on therear side of the main piston in order to clear the subpressure createdbehind the main piston when it is being brought to armed positionwhereby, except for the piston spring pressure, the diameter of saidleak hole determines the delay time of the arming movement.
 3. A safetyfuse according to claim 2, wherein the fuse casing has a hole on a levelwith an end of the firing pin for a sidewardly displaceable locking pinhaving a recess for the reception in safety position of the firing pinwhich has the lowest possible mass, said locking pin having a headabutting directly against the impact-sensitive body as long as thelocking pin striker functions safety stays in.
 4. A safety fuseaccording to claim 1, wherein a short tube with a hole, fins and drivingcharges can be attached to a bottom socket of the fuse and that the mainpiston is pushed inwardly by the pressure of the driving gases in thebarrel of a mortar during launch.